Post-traumatic stress disorder (PTSD), a chronic, disabling condition resulting from exposure to stressful traumatic events, is highly prevalent among military populations but also occurs frequently in the community. PTSD is characterized by a broad and persistent maladaptive physiological reaction with central and autonomic nervous system abnormalities and hormonal dysregulation. Persons with PTSD tend to report more CVD problems than those without, but little is known on the effects of PTSD on the cardiovascular system using objective measures. The main objective of this project is to clarify whether PTSD is associated with subclinical CVD and decreased heart rate variability (HRV), and the main determinants of this association, in a sample of 140 monozygotic and dizygotic twin pairs discordant for PTSD. Since twins share their genetic makeup (which is identical if they are monozygotic) and rearing environment while growing up, they are matched on numerous known and unknown potentially confounding factors. The specific aims are: (1) To investigate whether PTSD is associated with markers of subclinical vascular disease, including coronary flow reserve, measured by means of Positron Emission Tomography (PET), carotid intima-media thickness, and forearm flow-mediated vasodilation, both measured by ultrasound. (2) To investigate whether PTSD is associated with decreased heart rate variability measured by ambulatory electrocardiographic monitoring. (3) To determine the relative contributions of genetic and environmental influences to the association between PTSD and subclinical cardiovascular measures. The twins will be drawn from the Vietnam Era Twin (VET) Registry. Participants will travel to Emory where they will receive confirmation of PTSD status and undergo a comprehensive lifestyle and clinical evaluation and non-invasive CVD testing. Blood will also be drawn to determine the role of biological mediators such as neuro-hormonal status, inflammation and oxidative stress. Besides extending our knowledge on the long-term consequences of chronic psychological stress on the cardiovascular system, our results could have important clinical and public health implications. Efforts toward the prevention, early identification and treatment of PTSD and the identification of factors that mediate its adverse effects could reduce morbidity and mortality from CVD.